The present invention relates to a method and composition for use in treating subterranean formations. More particularly this invention relates to a method and formation control additive for use in treating subterranean formations containing clays and other fines. Most particularly, this invention relates to a formation control additive and method for use in fracturing a subterranean formation containing clays and other fines.
It is well known that the production of oil and gas is many times hindered by the presence of clays and other fines capable of swelling and/or migrating in the formation. The clays or fines may be already present or may be introduced into the formation during formation treating activity. In some instances, the clays and fines are quiescent causing no obstruction to the flow of hydrocarbons through the subterranean formation. However, when the clays or fines are distributed, the clays can swell or the fines can migrate through the formation until they become lodged in pore throats, thereby decreasing the permeability of the formation.
Unfortunately, most treatment activity associated with the production of oil and gas has the potential to disturb the quiescent clays and fines. For example, in a steam drive operation, steam is injected via one well and acts as a drive fluid to push oil through the formation to one or more offset wells. In a steam soaking operation, steam is injected via a well, the well is then shut in temporarily and allowed to soak, and subsequently production is commenced from the same well. In either instance, when steam reaches the subterranean formation, it at least partially condenses, thus exposing the formation to fresh water. Even though steam may act to mobilize the oil in the formation, if the formation contains fines and water-sensitive clays, the permeability of the formation can be reduced.
Other formation treatment operations such as fracturing, acidizing, perforating, drilling, waterflooding, as well as others, can disturb the clays and fines causing a loss of formation permeability.
Because oil and gas production can be effected by the presence of clays and other fines, the prior art is replete with examples of various methods and formation control agents designed to minimize clay swelling and fine migration. One idea has been to convert the clay from a swelling form by cation exchange to a less swelling form, by the addition of various known salts to the aqueous fluids utilized in the various treatment methods. Salts such as potassium chloride, sodium chloride, ammonium chloride and the like are typically dissolved in the aqueous fluid utilized to effect the formation treatment. While these salts are effective at protecting the formation, they can be detrimental to the performance of other constituents of the treatment fluid. Furthermore, it is difficult to dissolve the various salts in viscosified fluid due to the inability to effect adequate mixing for the large volumes of salts required in commercially available mixing equipment utilized in oil field services. Therefore, the salts are typically admixed with the aqueous fluid before admixture of any viscosifying or gelling agents to the aqueous fluid. These salts, however, may have a detrimental effect upon the viscosity yield by the gelling agent upon hydration in the aqueous fluid.
Other ideas for minimizing clay swelling and fines migration include the use in treatment fluids of nitrogen base compounds as described in U.S. Pat. Nos. 2,761,835 and 2,761,843, or by the use in treatment fluids of water-soluble anionic, cationic or non-ionic surfactants. These methods, however, have been found to be essentially ineffective particularly when these so-called treated formations are subjected to fresh water flooding operations.
Disclosed in U.S. Pat. No. 4,842,073 is the use in a treatment fluid of a tetra alkyl ammonium salt, wherein the alkyl groups are non-substituted and have from 1 to 4 carbon atoms.
While each of the prior art treatments to stabilize clays in a formation have met with some success in particular applications, the need exists for a further improved method for treating clay and fines in formations to minimize the adverse effect of clays and fines on the permeability of the formation, particularly when the clays and fines are contacted by a treatment fluid comprising water.
It is therefore an object of this invention to provide for a further improved formation control additive and method for treating a formation containing clays and fines.